September 23, 2008
Aged Brain Has Less Capacity To Feel Rewards?

A paper published in the US Proceedings of the National Academy of Sciences finds that reduced dopamine metabolism in the brain suggests that as we age we experience a reduced capacity to feel rewarded.

Here, by using 6-[18F]FluoroDOPA (FDOPA) positron emission tomography (PET) and event-related 3T functional magnetic resonance imaging (fMRI) in the same subjects, we directly demonstrate a link between midbrain dopamine synthesis and reward-related prefrontal activity in humans, show that healthy aging induces functional alterations in the reward system, and identify an age-related change in the direction of the relationship (from a positive to a negative correlation) between midbrain dopamine synthesis and prefrontal activity. These results indicate an age-dependent dopaminergic tuning mechanism for cortical reward processing and provide system-level information about alteration of a key neural circuit in healthy aging. Taken together, our findings provide an important characterization of the interactions between midbrain dopamine function and the reward system in healthy young humans and older subjects, and identify the changes in this regulatory circuit that accompany aging.

This seems like a big loss to me. We need stem cell therapies, gene therapies, and nanobot therapies that can go into our brains and repair the accumulated damage and restore youthful function.

Share |      Randall Parker, 2008 September 23 12:06 AM  Brain Aging


Comments
dougb said at September 23, 2008 4:26 AM:

Disagree....

here in maryland we are currently having a debate on the approval of slot machine parlors. Older people are definately more likely to get addicted to slots (an activity which bores the crap outta me). Also older people like bingo lotterys etc more. And they seem easier to please in general. Parkinsons results from a dopamine defict and one side effect of parkinsons drug's is a tendancy to gambling addiction.....normal people suddenly going on benders in vegas and losing everything. So if anything I would say the reward system is enhanced in older people. Perhaps the aged brain clear dopamine less rapidly leading to a longer or more severe "high".

cathy said at September 23, 2008 4:53 AM:

Maybe that's one reason why older people don't learn as fast as younger people.

James Bowery said at September 23, 2008 9:00 AM:

It makes evolutionary sense if older people serve as repositories of accumulated wisdom more than agents. Basically, as sample (experience) size increases the weight of the Bayesian Prior (prejudice/wisdom/bigotry/knowledge) increases.

A Stoner said at September 23, 2008 12:14 PM:

I doubt this has anything at all to do with addiction to slot machines.

Brian said at September 23, 2008 1:57 PM:

dougb,

The drugs which cause Parkinsons patients to become addicted to slot machiness are a class called dopamine agonists- Mirapex and Requip are two common examples. Dopamine plays a role in two brain systems/pathways- movement and reward. Parkinsons is caused when the dopamine rich neurons on the substantia nigra die off, this has a detrimental effect the nigro-straital dopamine pathway which plays a major role in the regulation of movement. However, Dopamine agonists are indiscrimiant in their effect on dopamine receptors- so Parkinsons patients on the drugs get an increase in both reward function and movement function; Hence the new found addictions to slots. The same drugs have been prescribed to individuals with "restless legs syndrome," with the same side effects.

Also, this study seems to correlate well the increased rates of suicide in individuals over the age of 65. Scary to think that perhaps depression IS just a part of aging. I can't think of any more important reason to develop brain rejuvenation therapies than this.

ADD said at September 23, 2008 2:49 PM:

dougb,

The problem with your hypothesis is that Parkinsonís drugs boost the reward system when they boost the dopamine levels. So it seems like it's the drugs and not aging that's causing the gambling.

People with Parkinsonís have a problem in a part of the frontal lobe called the basal ganglia. The Parkinsonís drugs boost the effects of dopamine in the basal ganglia, but have side effects because dopamine is used in the rest of the frontal lobe also. So they could feel pleasure from something that should get boring quickly.

A similar effect happens with ADHD medicine. Ritalin boosts dopamine in the cortex helping with focus and self control. But it also over stimulates the basal ganglia causing anxiety as a common side effect.

The problem is that drugs are not precise enough to target just one little subsystem in the brain. Any part of the brain that uses the same neurotransmitter gets knocked out of whack. There's nothing that can be done about this. It's just a question of whether the cure is worse than the disease or not. And the answer to that question is different for each patient.

I could also add that if dopamine is declining across the entire frontal lobe in old people, it should produce ADHD-like symptoms. Here's a list of ADHD symptoms:

According to Barcley (1991, Attention Deficit Disorder: A Clinical Workbook, NY: Guilford Press)

There are 5 features of observable behavior for someone who has ADHD:

1. Limited attention span - rapid boredom, frequent shifting form task to task, quick loss of concentration, failure to complete work assignments

2. Reduced impulse control/limited delay of gratifcation-unable to wait ones turn, living for the short-term vs long-term goal setting

3. Task irrelevant activity-fidgety, restless, excessive movement, trouble sitting still

4. Not good at following rules

5. Great variability regarding task performance- perform great one day, horrible the next on similar tasks, inconsistent


Symptom #2 has "compulsive gambler" written all over it.

Gillie said at September 23, 2008 5:47 PM:

There's an old saying that when you're a real grownup, "you're old enough for your wants not to hurt you." That's just a folksy way of saying that the stuff that seemed so thrilling as a younster just isn't as appealing later on, perhaps because it's true that "the thrill is gone."

Tj Green said at September 24, 2008 4:27 PM:

I blame a dysfunctional blood brain barrier on most of the brain disorders associated with aging.

Joe K. said at October 3, 2008 2:24 PM:

RP - Is McCain getting an edge from his Neuro 1 supplement? I checked the ingredient list, it's pretty long. Is this snake oil for seniors or is there some benefit to it?

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